An electrical camshaft adjuster of an internal combustion engine is known from DE 10 2005 018 956 A1 or DE 102 48 355 A1. The camshaft is driven in semi revolution from the crankshaft, for which purpose a camshaft drive wheel of the camshaft is coupled to the crankshaft. An adjusting gear between the camshaft and camshaft drive wheel makes it possible to adjust the phase position of the camshaft drive wheel and camshaft. The adjusting gear may be designed, for example, as a double planetary gear or as a harmonic drive gear.
DE 103 52 255 A1 shows a camshaft adjuster with an adjusting drive designed as a triple-shaft gear. The electric motor is arranged separately in space from the adjusting shaft of the adjusting gear—the adjusting torque is transmitted by means of a flexible shaft.
In the event of failure of the activation electronics and/or of the electric motor, the camshaft adjuster must bring the camshaft into a neutral position or into an emergency running position, and this relative rotation defined in this way between the camshaft drive wheel and the camshaft must be maintained in order to continue to operate the internal combustion engine or so that it can be operated again after being stopped.
EP 1 504 172 B1 describes a camshaft adjuster in which, in the event of failure of the servomotor, it exerts a braking action (that is to say, looses rotational speed with respect to the camshaft drive wheel) and thus causes an end position, a failsafe position, to be assumed. The maximum advance or retard position of the camshaft is therefore assumed. It is not described how the camshaft is held in this position. Nor are any measures provided if the servomotor, in the event of failure or in the event of failure of the activation electronics, generates only insignificant braking torque. In these cases, the failsafe position is sometimes not reached or there is no assurance that the camshaft remains in the failsafe position or leaves this position in an uncontrolled way.
PCT/EP2011/050861 shows a camshaft adjuster with a bias spring which presses the camshaft adjuster back into a corresponding end position (maximum advance position or maximum retard position of the camshaft). This spring is active over the entire range of adjustment, although this is not advantageous in terms of energy consumption. If in the event of failure, the electric adjusting motor generates a correspondingly high braking torque (for example, due to a short circuit in the winding), the desired limit stop cannot be reached by means of a return spring of this type.
DE 103 32 264 A1 describes a failsafe system of a camshaft adjuster which has displaceable mechanical limit stops. These limit stops are prestressed in one direction in each case by means of a spring, in such a way that they correspondingly reduce the range of adjustment in the direction of the failsafe position, that is to say the maximum retard or advance position of the camshaft adjuster is reduced. During fault-free normal operation, these displaceable stops are blocked by means of a mechanical device, so that the entire range of adjustment of the camshaft adjuster can be utilized.